//Swift 中的控制流语句有: while, if, guard, switch, for in, where break, continue
//一. For in
//用于遍历 Strings, Array, dictionary, Set, ranges等
//for in 循环中的局部变量如 name 是一个 let 值,每次创建循环都会创建, 如果用不到局部变量的值,可以用下划线代替
//1. for in 遍历数组
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names {
print(name)
}
//2. for in 遍历字典
let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
for (animalName, legCount) in numberOfLegs {
print("\(animalName)s have \(legCount) legs")
}
//3. for in 遍历 range
for index in 1...5 {
print("\(index) times 5 is \(index * 5)")
}
//4. 不用局部变量的值, 用 _ 代替
let base = 3
let power = 10
var answer = 1
for _ in 1...power {
answer *= base
}
let minutes = 60
for tickMark in 0..<minutes {
print(tickMark)
}
//5. 间隔遍历
//开区间用 stride(from:to:by:), 不包括最后一位
let minuteInterval = 5
for tickMark in stride(from: 0, to: minutes, by: minuteInterval) {
print(tickMark) //(0, 5, 10, 15 ... 45, 50, 55)
}
//闭区间用 stride(from:through:by:), 包括最后一位
let hours = 12
let hourInterval = 3
for tickMark in stride(from: 0, through: 12, by: hourInterval) {
print(tickMark) //0, 3, 6, 9, 12
}
//二. while
//分为 while 和 repeat-while
//while
//while condition {
// statements
//}
//repeat-while
//repeat {
// statements
//} while condition
//三. Switch 和 if
//1. switch 执行一次匹配语句停止,不需要写 break, 但仍然可以使用break 跳出语句
//case(包括 default) 语句中至少有一条语句,不允许为空
//fallthrough 相当于 break当前语句,继续往下判断
let someCharacer: Character = "z"
switch someCharacer {
case "a":
print("The first letter of the alphabet")
case "z":
print("The last letter of the alphabet")
fallthrough
default:
print("Some other character")
}
//2. 一个case 匹配多个值, 用逗号隔开
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a", "c", "d", "f", "g", "h", "j", "k", "l", "m",
"n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
print("The letter a")
default:
print("Not the letter A")
}
//3. case使用ranges匹配
let approximateCount = 62
let countedThings = "moons orbiting Saturn"
let naturalCount: String
switch approximateCount {
case 0:
naturalCount = "no"
case 1..<5:
naturalCount = "a few"
case 5..<12:
naturalCount = "several"
case 12..<100:
naturalCount = "dozens of"
case 100..<1000:
naturalCount = "hundreds of"
default:
naturalCount = "many"
}
print("There are \(naturalCount) \(countedThings).")
// Prints "There are dozens of moons orbiting Saturn."
//4. case 使用tuples匹配
//可以用通配符 _ , 匹配任意值
//Swift 允许所有的 case 都匹配,但是只会执行第一个匹配的,其它的忽略
let somePoint = (0, 0)
switch somePoint {
case (0, 0):
print("\(somePoint) is at the origin")
case (_, 0):
print("\(somePoint) is on the x-axis")
case (0, _):
print("\(somePoint) is on the y-axis")
case (-2...2, -2...2):
print("\(somePoint) is inside the box")
default:
print("\(somePoint) is outside of the box")
}
// Prints "(1, 1) is inside the box"
//5. case值绑定,switch case 可以为它比较的值命名一个临时变量或常量在 case 语句中使用
let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
print("on the x-axis with an x value of \(x)")
case (0, let y):
print("on the y-axis with a y value of \(y)")
case let (x, y):
print("somewhere else at (\(x), \(y))")
}
// Prints "on the x-axis with an x value of 2"
//6. where, 可以用于在 case 语句中添加判断条件
let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
print("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
print("(\(x), \(y)) is on the line x == -y")
case let (x, y):
print("(\(x), \(y)) is just some arbitrary point")
}
// Prints "(1, -1) is on the line x == -y"
//7. 复合 case 语句
//一个 case 匹配多个值, 每个值称为一个 pattern, 可换行
let someCharacter: Character = "e"
switch someCharacter {
case "a", "e", "i", "o", "u":
print("\(someCharacter) is a vowel")
case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m",
"n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
print("\(someCharacter) is a consonant")
default:
print("\(someCharacter) is not a vowel or a consonant")
}
// Prints "e is a vowel"
//8. 复合 case 语句值绑定(value bindings)
//每个 pattern 必须包含一个相同的 binding, 每个 binding必须从每个 pattern 中获取一个相同类型的值,确保在 case 语句体中,始终可以得到一个相同类型的值.
//如下例每个 pattern 中都有一个binding 对应 distance 常量, distance 在每个 pattern 中都可以得到一个相同类型的值
let stillAnotherPoint = (9, 0)
switch stillAnotherPoint {
case (let distance, 0), (0, let distance):
print("On an axis, \(distance) from the origin")
default:
print("Not on an axis")
}
// Prints "On an axis, 9 from the origin"
//9. 控制流传递语句(Control Transfer Statements)
//可以改变代码的执行顺序,把控制流从一部分代码转到另一部分,
//Swift 中有五个控制流传递语句: continue, break, fallthrough, return, throw
//continue, break, fallthrough 用于一般控制流
//return 用于函数 Functions
//throw 用于函数中抛出错误
//(1) continue, 结束当前这一次遍历
let puzzleInput = "great minds think alike"
var puzzleOutput = ""
let charactersToRemove: [Character] = ["a", "e", "i", "o", "u", " "]
for aChar in puzzleInput {
if charactersToRemove.contains(aChar) {
continue
}else {
puzzleOutput.append(aChar)
}
}
print(puzzleOutput)
//(2) break, 用于 conditional 语句或者 loop 中,结束整个控制流
let numberSymbol: Character = "三" // Chinese symbol for the number 3
var possibleIntegerValue: Int?
switch numberSymbol {
case "1", "١", "一", "๑":
possibleIntegerValue = 1
case "2", "٢", "二", "๒":
possibleIntegerValue = 2
case "3", "٣", "三", "๓":
possibleIntegerValue = 3
case "4", "٤", "四", "๔":
possibleIntegerValue = 4
default:
break
}
//(3) 条件 binding, 必须用可选类型
if let integerValue = possibleIntegerValue {
print("The integer value of \(numberSymbol) is \(integerValue).")
} else {
print("An integer value could not be found for \(numberSymbol).")
}
// Prints "The integer value of 三 is 3."
//(4) fallthrough
//Swift case 语句匹配成功自动结束不需要写 break, 如果要继续向下匹配用 fallthrough
let integerToDescribe = 5
var description = "The number \(integerToDescribe) is"
switch integerToDescribe {
case 2, 3, 5, 7, 11, 13, 17, 19:
description += " a prime number, and also"
fallthrough
default:
description += " an integer."
}
print(description)
// Prints "The number 5 is a prime number, and also an integer."
//(5) 标签语句
//break, continue 可用于 conditional 和 loop, 在嵌套中为了区分break 作用于那个 control flow,可以给 loop 或者 conditional 语句加一个标签
//在控制流关键词前加一个标签 label后面加一个冒号
//label name: while condition {
// statements
//}
let finalSquare = 25
var board = [Int](repeating: 0, count: finalSquare + 1)
board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02
board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08
var square = 0
var diceRoll = 0
gameLoop: while square != finalSquare {
diceRoll += 1
if diceRoll == 7 { diceRoll = 1 }
switch square + diceRoll {
case finalSquare:
// diceRoll will move us to the final square, so the game is over
break gameLoop
case let newSquare where newSquare > finalSquare:
// diceRoll will move us beyond the final square, so roll again
continue gameLoop
default:
// this is a valid move, so find out its effect
square += diceRoll
square += board[square]
}
}
print("Game over!")
//上例中 break, 可以终止 switch也可以终止 loop,用 label 明确是终止 loop 而不是 switch.
//continue 只作用于 loop, 后边可以不注明跳出那个控制流
//10. guard 语句
//用法类似于 if, 和 if 不同的是后边必须有一个 else 语句,满足条件,执行 guard 语句之后的代码,否则执行 else 中的代码
func greet(person: [String: String]) {
guard let name = person["name"] else {
return
}
print("Hello \(name)!")
guard let location = person["location"] else {
print("I hope the weather is nice near you.")
return
}
print("I hope the weather is nice in \(location).")
}
greet(person: ["name": "John"])
// Prints "Hello John!"
// Prints "I hope the weather is nice near you."
greet(person: ["name": "Jane", "location": "Cupertino"])
// Prints "Hello Jane!"
// Prints "I hope the weather is nice in Cupertino."
//11. 检查 API 的可得性
//Swift 内置支持检查,编码器使用SDK(software development kit) 中的信息来判断代码中使用的 API(application programming interface)在部署目标中可得,如果不可得会编译报错